Permanent magnet strong field separator

ABSTRACT

For concentrating particularly weakly magnetic minerals there is provided a rotating cylinder or drum having at its circumference a number of magnetic pole gaps created by pole shoes and adjacent permanent magnets having a great coercive force. Inside the cylinder there is provided a separate permanent magnet system causing an essential change in the magnetic field within the gaps as the section in question of the cylinder circumference passes a certain point. Said change in the field releases the magnetic material attached to the cylinder by the magnetic force. The separate magnet system preferably comprises a second cylinder provided with magnets at equal distances from each other as those at the outer working cylinder and rotating in synchronism with said outer cylinder.

United States Patent Laurila June 3, 1975 PERMANENT MAGNET STRONG FIELDSEPARATOR Primary Examiner-Robert Halper Attorney, Agent, or Firm-Browdyand Neimark [75] Inventor: Erkki A. Laurila, Helsinki, Finland Bermeco0y, Helsinki, Finland May 21, 1973 [57] ABSTRACT For concentratingparticularly weakly magnetic miner- [73] Assignee:

Filed:

Appl.

,305 als there is provided a rotating cylinder or drum having at itscircumference a number of magnetic pole gaps created by pole shoes andadjacent permanent [30] Foreign Application Priority Data May 26, l972Finland.....

magnets having a great coercive force. Inside the cyl 1436/72 inderthere is provided a separate permanent magnet system causing anessential change in the magnetic field within the gaps as the section inquestion of the cylinder circumference passes a certain point. Said 02 a3 1 B Q12 9 0 &3 2N w "m m a m in "m0. 9 "0 m nmf L C min UI-F 111 2 oo555 [ll change in the field releases the magnetic material at- 209/220tached to the cylinder by the magnetic force. The separate magnet systempreferably comprises a second cylinder provided with magnets at equaldistances from each other as those at the outer working cylinder androtating in synchronism with said outer cylinder.

335/295 lsraelson.................v...... 335/295 x Clams 2 DrawmgF'gures 3,223.898 3,231,789 l/l966 Engelsted.... 3,4523 I0 6/1969PERMANENT MAGNET STRONG FIELD SEPARATOR BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to magneticseparators and more particularly to separators for weakly magneticminerals, wherein concentrating takes place at the circumference of arotating cylinder or drum.

2. Description of the Prior Art The attraction ofa magnetic field on aferromagnetic or paramagnetic particle is known to be proportional tothe product of the absolute value H of the magnetic field strength andits gradient, i.e., the quantity [Hl grad lH l Thus, the separators usedfor separating weakly magnetic minerals must have both a strong field,which is the reason for the name strong field separator, and means withwhich this field can be strongly reversed at appropriate points, whilethe separation of strongly ferromagnetic materials is easier.

In one known apparatus for separating the latter materials, concentrateis fed onto the circumference of a rotating cylinder which has beenprovided with permanent magnet bars at regular intervals so that theirmagnetic fields are radial and alternately reverse. The magneticmaterial is separated by means of a smaller cylinder which has beenfitted outside the principal cylinder and rotates synchronically withit. The peripheral surface of the smaller cylinder has been respectivelyfitted with iron rods which, when coming close to the said permanentmagnet bars, momentarily strengthen the magnetic field and cause themagnetic material to pass from the surface of the cylinder provided withmagnet bars onto the separation cylinder, from where the said stronglymagnetic part is then recovered.

The known separators for weakly magnetic materials have usually beenprovided with electric magnets to provide a sufficiently extensivefield. In addition, these separators have been provided with some movingpart which, when it is in the magnetic field, causes the field toconverge at certain points and, when it comes outside the range of thefield, loses its magnetism, thereby making it possible for the magneticmineral which has become attached to the convergence points to becomedetached.

SUMMARY OF THE INVENTION The present invention provides a magneticseparator of the character previously described, comprising a rotatingcylinder or drum on the outer surface of which the concentrate isseparated,

a number of pole gaps created on the cylinder surface by means of poleshoes linked to magnetic possessing a great coercive force, and

a separate multi-pole system with permanent magnets provided inside saidcylinder for causing an essential change of the magnetic field withinthe pole gaps as they pass a certain point at the cylindercircumference.

The object of the present invention is thus a strong field separatorstructure in which the magnetic field is created with permanent magnets.In principle, any permanent magnet materials with a sufficiently highenergy product are practicable, but it is essential to resort to oxidemagnets which are magnetically hard, i.e., possess a great coerciveforce. For example, ceramic barium ferrite and strontium ferritemagnets, such as Ferroxdure 330, Indox 5, lndox 8 etc., already make avery practical structure possible, but the construction principle setforth in the invention proves even more advantageous when, for example,CoSm or other lanthanide magnets with a coercive force of more than 5000Oe and an efficiency of IO 20 million GsOe are used.

Thus. according to the invention, a great number of pairs of poles, inthe field between which the quantity IHl grad [H l is high, are createdwith such magnets in the working area, such as a cylinder surface. Theessential point of the invention is the arrangement by which themagnetic field, at an appropriate stage, is entirely extinguished or atleast weakened to the extent that the weakly magnetic mineralconcentrate which has become attached to the field can be released. Insome cases it may be advantageous even to momentarily reverse themagnetic field at the concerned point at the cylinder circumference.

This change of the magnetic field, or actually the conduction of theflux along another path, takes place according to the invention with thehelp of a reversely magnetized system consisting of permanent magnets.The system may preferably include another cylinder which is situatedinside the working cylinder, rotates synchronically with it, and touchesor very nearly touches it at an appropriate point and which has beenrespectively provided with magnetic poles at the same intervals as onthe working cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows an apparatus according tothe invention with two cylinders linked to each other one inside theother, and

FIG. 2 shows a detail of FIG. 1 on an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the apparatus according tothe figures, the actual working unit consists of a cylinder 1 which hasa relatively long diameter and rotates in the direction indicated by thearrow. Pole gaps parallel to the side line of the cylinder have beencreated on the cylinder surface according to the construction principleindicated in the figure. It would also be possible to make the pole gapsparallel to the cylinder circumference. The active parts are permanentmagnets 2 made of an oxide or Ianthanide magnet material and which arealternately magnetized in reverse directions. T-shaped iron rails 3 formthe pole shoes; a sufficiently strong field strength can be obtained inthe narrow gaps between the pole shoes, for example over 10 k0, whilethe field gradient receives a very high value. When some granularmaterial or suspension is fed onto the cylinder surface, ferromagneticand paramagnetic particles become attached to the cylinder surface atthe pole gaps. By using blowing, or water sprays when a suspension isconcerned, a considerable portion of the accompanying non-magneticmaterial can be removed so that finally only a relatively pureconcentrate remains attached to the pole gaps. FIG. 1 illustrates thefeeding of suspension with feeding trough 4, the suspension outlet withits thresholds 5 where the concentrate particles which remain in theoutflowing suspension still have an opportunity to become attached tothe magnetic field of the cylinder, and washing system 6 consisting ofwater sprays. It is natural that in this wet separator the rotativevelocity of the cylinder is so low that the water and suspension flowdownwards against the rotational direction of the cylinder. Theconcentrate which has become attached at the magnet gaps between thepole shoes on the cylinder surface is removed with second magneticcylinder 7. Magnets 8 (FIG. 2) have been provided on its circumferenceso that the mutual distance between their pole shoes 9 or magnet ends isthe same as the distance between pole shoes on the surface ofcylinder 1. When the cylinders rotate in the directions indicated byarrows, opposite poles will always face each other. As explained in moredetail in the description relating to FIG 2, the field then disappearsfrom the magnet gap between pole shoes 3 when permanent magnet 2 is inthe position closest to the surface of cylinder 7, if magnets 8 ofcylinder 7 have appropriate dimensions. This appropriate dimensioningcan be calculated on the basis of the general theory concerning magneticcircuits. The magnetic potential corresponding to the state of magnets 8at a given moment must be sufficient to create the necessary flux overthe magnet gap between the cylinders. The width of the pole shoe 3 edgesinside and in a tangential direction of the cylinder 1 is chosen to bemore than l/n of the width of permanent magnets 2 measured in thedirection of cylinder 1 radius, where n indicates the ratio between thesaturation induction of the pole shoe material and the remenantinduction of the permanent magnet material. When the field disappears ina magnet gap between pole shoes 3, the concentrate attached to itbecomes detached either owing to centrifugal force (in dry separators)or in the manner indicated in the figure with the help of water spray lldirected from between bridge l and the surface of cylinder 1. Thedetached concentrate is then removed along bridge 10.

To diminish constructional problems, the diameter of cylinder 7 ispreferably less than half the inner diameter of cylinder 1. Theplacement of counter-cylinder 7 inside the working cylinder providesmainly two advantages which are closely linked to each other. The magnetgap between the cylinders can then be small and the extinction of themagnetic field in the pole distances on the cylinder surface can beachieved without the magnets of cylinder 7 having to become unreasonablyoversized. Constructionally it is also very advantageous that there areno devices which inconvenience the flow and treatment of material on theouter surface of the cylinder or in its vicinity. This would be the caseif the counter-cylinder were placed outside the working cylinder. FIG. 2shows an enlarged section of the contact point between the cylinders.The arrows indicate the directions of the the internal magnetic fieldsof permanent magnets 2 of outer cylinder 1 and permanent magnets 8 ofinner cylinder 7. When the point in question on the outer cylinder isfar from the circumference of the inner cylinder, the magnetic path onthe outer cylinder is closed mainly owing to the narrow magnet gapbetween the expanded ends of pole shoes 3. When, again, the point inquestion comes essentially in contact with the magnets on thecircumference of the inner magnets, as shown in the figure, these twomagnet systems form a closed magnet circuit, i.e., the entire flux of aworking cylinder magnet runs through the respective counter-cylindermagnet, and thereby the flux and field in the magnet gap on the cylindersurface are extinguished. By an appropriate dimensioning of the magnetsand the poles the flux in the said magnet gaps can even becomemomentarily reversed.

One prerequisite for an appropriate operation is now that the fluxcorresponding to the remanent induction of the magnets on cylinder 7 isgreater than the flux corresponding to the remanent induction of magnets2. The continuous attraction between opposite magnetic poles ensures thesynchronic rotation of cylinders l and 7.

What is claimed is:

1. A permanent magnet separator particularly for separating weaklymagnetic materials from nonmagnetic materials, comprising:

a first hollow rotating cylinder, having inner and outer surfaces,composed of a plurality of substantially rectangular solid permanentmagnets each arranged in a parallel relation to the side line of saidcylinder and a plurality of pole pieces each substantially identicallyshaped and spaced intermediate said permanent magnets, thereby formingon said inner surface alternate substantially parallel sectionsconsisting of said magnets and pole pieces, said permanent magnets beingalternately reversely magnetized; and

shunting means, including a separate rotating multipole permanent magneteccentrically mounted within said first cylinder, for shunting themagnetic field of said pole pieces of said first cylinder by cooperationbetween said shunting means and said pole pieces of said first cylinderas said pole pieces of said first cylinder come into a certain positionin relation to said shunting means;

said separate permanent magnet comprising a second rotating cylinderwith alternating reversely magnetized permanent magnets and pole piecesin which the distance between the magnetic pole pieces is the same asthe distance between the magnetic pole pieces of said inner surface andwherein the remanent flux of said permanent magnets on said secondcylinder is greater than the remanent flux of said permanent magnets onsaid first cylinder, said second cylinder being synchronized with saidfirst cylinder so that said magnetic pole pieces thereof always faceoppositely magnetized pole pieces on said first cylinder at said certainposition.

2. The separator of claim 1, wherein the width of each of said polepieces inside and in tangential direction of said first cylinder is morethan 1/n of the width of each of said permanent magnets measured in thedirection of said first cylinder radius, where it indicates the ratiobetween the saturation induction of the pole shoe material and theremenant induction of the permanent magnet material.

3. A separator according to claim 1, wherein said magnets on said firstand second cylinders are oxide permanent magnets.

4. The separator of claim 3 wherein said oxide permanent magnets arecomposed of barium ferrite.

5. The separator of claim 3 wherein said oxide permanent magnets arecomposed of strontium ferrite.

6. A separator according to claim 1, wherein said magnets on said firstand second cylinders are lanthanide permanents magnets.

7. A separator according to claim 1, wherein the magnetic strength ofsaid permanent magnets of said second cylinder in relation to themagnetic strength of said permanent magnets of said first cylinder issuch that shunting essentially weakens the magnetic field of said polepieces of said first cylinder at the said certain position.

8. A separator according to claim 1, wherein the magnetic strength ofsaid permanent magnets of said second cylinder in relation to themagnetic strength of said permanent magnets of said first cylinder issuch that shunting essentially extinguishes the entire magnetic field ofsaid pole pieces of said first cylinder at the said certain position.

9. A separator according to claim 1, wherein the magnetic strength ofsaid permanent magnets of said second cylinder in relation to themagnetic strength of said permanent magnets of said first cylinder issuch that shunting momentarily makes the magnetic field of said polepieces of said first cylinder weakly reverse at the said certainposition.

10. The separator of claim 1 wherein the said pole pieces on said firstcylinder are formed in substantially the shapes of a T and are arrangedin a spaced relation to the said solid rectangular permanent magnetssuch that the cross of the T's form the outer circumference of the saidfirst cylinder and said crosses of said T's of adjacent ones of saidpole pieces do not abut one another, thereby forming with said permanentmagnets substantially parallel slots in the outer surfaces of said firstcylinder.

1. A permanent magnet separator particularly for separating weaklymagnetic materials from non-magnetic materials, comprising: a firsthollow rotating cylinder, haviNg inner and outer surfaces, composed of aplurality of substantially rectangular solid permanent magnets eacharranged in a parallel relation to the side line of said cylinder and aplurality of pole pieces each substantially identically shaped andspaced intermediate said permanent magnets, thereby forming on saidinner surface alternate substantially parallel sections consisting ofsaid magnets and pole pieces, said permanent magnets being alternatelyreversely magnetized; and shunting means, including a separate rotatingmultipole permanent magnet eccentrically mounted within said firstcylinder, for shunting the magnetic field of said pole pieces of saidfirst cylinder by cooperation between said shunting means and said polepieces of said first cylinder as said pole pieces of said first cylindercome into a certain position in relation to said shunting means; saidseparate permanent magnet comprising a second rotating cylinder withalternating reversely magnetized permanent magnets and pole pieces inwhich the distance between the magnetic pole pieces is the same as thedistance between the magnetic pole pieces of said inner surface andwherein the remanent flux of said permanent magnets on said secondcylinder is greater than the remanent flux of said permanent magnets onsaid first cylinder, said second cylinder being synchronized with saidfirst cylinder so that said magnetic pole pieces thereof always faceoppositely magnetized pole pieces on said first cylinder at said certainposition.
 1. A permanent magnet separator particularly for separatingweakly magnetic materials from non-magnetic materials, comprising: afirst hollow rotating cylinder, haviNg inner and outer surfaces,composed of a plurality of substantially rectangular solid permanentmagnets each arranged in a parallel relation to the side line of saidcylinder and a plurality of pole pieces each substantially identicallyshaped and spaced intermediate said permanent magnets, thereby formingon said inner surface alternate substantially parallel sectionsconsisting of said magnets and pole pieces, said permanent magnets beingalternately reversely magnetized; and shunting means, including aseparate rotating multipole permanent magnet eccentrically mountedwithin said first cylinder, for shunting the magnetic field of said polepieces of said first cylinder by cooperation between said shunting meansand said pole pieces of said first cylinder as said pole pieces of saidfirst cylinder come into a certain position in relation to said shuntingmeans; said separate permanent magnet comprising a second rotatingcylinder with alternating reversely magnetized permanent magnets andpole pieces in which the distance between the magnetic pole pieces isthe same as the distance between the magnetic pole pieces of said innersurface and wherein the remanent flux of said permanent magnets on saidsecond cylinder is greater than the remanent flux of said permanentmagnets on said first cylinder, said second cylinder being synchronizedwith said first cylinder so that said magnetic pole pieces thereofalways face oppositely magnetized pole pieces on said first cylinder atsaid certain position.
 2. The separator of claim 1, wherein the width ofeach of said pole pieces inside and in tangential direction of saidfirst cylinder is more than 1/n of the width of each of said permanentmagnets measured in the direction of said first cylinder radius, where nindicates the ratio between the saturation induction of the pole shoematerial and the remenant induction of the permanent magnet material. 3.A separator according to claim 1, wherein said magnets on said first andsecond cylinders are oxide permanent magnets.
 4. The separator of claim3 wherein said oxide permanent magnets are composed of barium ferrite.5. The separator of claim 3 wherein said oxide permanent magnets arecomposed of strontium ferrite.
 6. A separator according to claim 1,wherein said magnets on said first and second cylinders are lanthanidepermanents magnets.
 7. A separator according to claim 1, wherein themagnetic strength of said permanent magnets of said second cylinder inrelation to the magnetic strength of said permanent magnets of saidfirst cylinder is such that shunting essentially weakens the magneticfield of said pole pieces of said first cylinder at the said certainposition.
 8. A separator according to claim 1, wherein the magneticstrength of said permanent magnets of said second cylinder in relationto the magnetic strength of said permanent magnets of said firstcylinder is such that shunting essentially extinguishes the entiremagnetic field of said pole pieces of said first cylinder at the saidcertain position.
 9. A separator according to claim 1, wherein themagnetic strength of said permanent magnets of said second cylinder inrelation to the magnetic strength of said permanent magnets of saidfirst cylinder is such that shunting momentarily makes the magneticfield of said pole pieces of said first cylinder weakly reverse at thesaid certain position.